Metacarpal bones
The middle hand bones (lat. Ossa metacarpi) consist of five tubular bones. They are each divided into a base, a shaft and a head. The metacarpal bones form the connection between the carpal bones and the finger bones.
Anatomy
Anatomy of the metacarpal bones
The metacarpals are five tubular bones positioned between the carpal bones and the phalanges. They form the basic bony structure of the metacarpus. For the anatomical designation of the five bones, they are numbered from lateral to medial:
.
The os metacarpale primum (os metacarpale I) has a connection to the thumb bones as well as to the large polygon.
The longest metacarpal bone is the os metacarpale secundum (os metacarpale II). It is connected to the large and small polygon and carries the bones of the index finger.
Through the os metacarpale tertium (os metacarpale III) the head bone and the middle finger bones are connected to each other.
The ring finger is carried by the os metacarpale quartum (os metacarpale IV). This metacarpal bone articulates with the capitate bone and the hamate bone.
The last metacarpal bone, the os metacarpale quintum (os metacarpale V), is connected to the hooked bone and carries the bones of the little finger.
The individual bones are divided into three structures. The base ossis metacarpus has a cubic shape and is connected to the distal surfaces of the carpal bones. The base, the proximal end piece, is significantly thicker than the shaft that follows it. The long shaft of the metacarpal bones is called the corpus ossis metacarpi. It has an approximately triangular cross-section. The side of the metacarpal bones facing the phalanges is called caput ossis metacarpi and has a cartilaginous surface which is convex.
Der kürzeste dieser Röhrenknochen ist der Os metacarpale I. Der daneben angeordnete Os metacarpale II ist der längste Mittelhandknochen. Daraufhin nimmt die Länge der einzelnen Mittelhandknochen zur Ulna hin ab.
Funktion
Die Mittelhandknochen bilden die knöcherne Grundlage der Handfläche. Da die Mittelhand aus einzelnen Röhrenknochen,die strahl-ähnliche verlaufen, gebildet wird, ist die Elastizität der Hand gegeben. Durch die etwas abgespreizte Stellung des Os metacarpale I wird die prägnate abstehende Stellung des Daumens ermöglicht.
Entstehung
Die Mittelhandknochen werden jeweils durch eine Epiphyse und eine Diaphyse gebildet. Die Verknöcherung der Schäfte der Mittelhandkncohen findet bereits ab der neunten Embryonalwoche statt. Die Verschmelzung der Epiphysenkerne mit den Schaftabschnitten findet erst zwischen dem 16. und 18. Lebensjahr statt.
